The present invention relates to a method for quantitative determination of the fat content of a fat-containing sample.
It is known to determine the fat content in fat-containing samples, in particular milk samples, by infrared absorption techniques. Infrared absorption methods and apparatus for determining fat content in milk are described e.g. by Goulden, J. D. S.: British Pat. No. 989,617, Goulden, J. D. S.: J. Sci. Food Agric., 7, 609 (1956), Goulden, J. D. S.: Nature, 191, 905 (1961), Goulden, J. D. S.: J. Dairy Res, 31, 273 (1964), Goulden, J. D. S.: J. Soc. Dairy Techn., 17, 28 (1964), Grappin R., Jeunet R.: Le Lait, 52, 325 (1972), in a thesis by John Shields submitted for the degree of Bachelor of Philosophy at the University of York, November 1975, by Grappin R., Jeunet R.: Le Lait, 56, 498 (1976), Grappin R., Jeunet R.: Le Lait, 558, 1-16, (1976), in U.S. Patent Application No. 3,161,768 and U.S. Patent Application No. 931,621.
The principle of the infrared fat determination is based on measuring the absorption of the infrared light in the triglyceride carbonyl band at 5.73 .mu.m. In this waveband, the spectral influence of other components present in the sample, in particular protein and lactose, is low as they show no absorption, and hence, the absorption measured in the said band gives a good measure of the number of fat molecules in the sample.
The accuracy of the milk fat determination by the infrared method is of decisive importance to the usefulness of the method, as the measured results are used as basis for e.g. milk payment. It has been found, however, that the weight percentage of fat determined by the infrared method varies with varying chemical composition of the fat, for example due to seasonal variations, variations in feedstuff and breed of the milking cows, and such variations present a serious problem limiting the usefulness of the infrared absorption method and the acceptability of the method by the authorities in certain territories. Variations in fat composition require a frequent calibration of infrared milk analyzers against the chemical standard methods.